As you say it is outrageous that the police can and do trump up charges against people, and the courts tend to believe them rather than the accused. I know this happens because friends been involved in several instances during the course of my life. On two of these occasions I am pleased to say that the court found in my friends' favour, and on one the police were clearly lying (I was called as an expert witness) and costs were awarded against them.

It is, however, more the fault of the politicians who insist on ridiculous and arbitrary targets for the police so that they can claim to have reduced "crime" when it comes to voting time. Motorists are easy game because, as you say, it is hard to disprove something like you were using a mobile phone, or eating a packet of crisps or something. Unfortunately, contrary to what one might hope, the new PCCs will are likely only to make matters worse. By the way, it amuses me when I often see a car parked on a double yellow line with its left indicator and brake lights on, and the driver on a mobile phone. Little do they realise they are then committing two offences instead of one if they had continued driving. Furthermore I think they have more chance of been spotted as they are a sitting target.